How do atheists justify assumptions such as: logic is reliable?

Some theists consider that their god is the guarantor of the truth of suppositions that we all make in order to be able to relate to the world. For example: 'logic is reliable’.

How do you, as an atheist, justify this kind of basic assumption (if at all)?

Posted: August 17th 2007

bitbutter www

It’s a mistake to try to explain the existence of something if that something is axiomatic.

Theists wanting to claim that logic somehow 'comes from’ their god commit the fallacy of stealing the concept. Any god that might exist is automatically contingent on the law of identity ('a thing is what it is’).

To an atheist it seems intuitively obvious that the fact that we can use intangible tools like logic doesn’t mean that a god is behind them. The suggestion that one particular god has to be given the credit is even more absurd. But this is exactly the kind of of claim made by adherents to the presuppositionalist school of apologetics. This approach attempts to attack the validity of non-Christian reason and can wrong-foot you if you’re not familiar with the tactics.

Tell-tale signs that you’re dealing with a presuppositionalist include use of the key phrases 'atheists can’t account for [reason/logic/morality]’ and 'the impossibility of the contrary’.

I think presuppositionalists are well answered by the insights offered by objectivist atheology. The article How The Claim 'God Exists’ Contradicts Itself is a particularly good example of a simply stated problem that defeats the presuppositionalist.

Posted: September 21st 2007

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George Locke

First I’ll give a simple rebuttal, then i’ll provide a more thorough treatment.

I’ve got three keys on my keychain. One of them opens up the door in front of me. I try the first two; they don’t work. What kinds of assumptions do I have to make in order to know that the third key will open the door? If you think such assumptions need justification, well, then we haven’t got anything to talk about because you’re operating on the principle that nothing whatever can be proven and therefore language is meaningless.

A more rigorous treatment of the problem reveals that the question is more or less nonsense. The questioner asks us to justify the statement “logic is reliable”, or else capitulate that the statement is an unprovable assumption. Unfortunately, this doesn’t make any sense.

First, I’ll examine what it would mean if logic were unreliable, then show that if you can only ask whether logic is reliable if logic is reliable. According to the University of Hong Kong’s philosophy department, logic is “the study of the principles of correct reasoning”. Under this definition, if logic were unreliable, meaning human understanding of 'the principles of correct reasoning’ is unreliable, then we humans wouldn’t be able to distinguish good reasoning from bad reasoning (at least not reliably, which is essentially as bad as not at all since everything becomes suspect). Austin Cline from Brian’s link confirms this interpretation, “Logic is what allows us to distinguish correct reasoning from poor reasoning.”

(You might argue that we are in fact unable to reliably distinguish good arguments from bad, otherwise why is there so much disagreement? The short answer is that while logic is required for telling when an argument’s conclusion is sound, it is not sufficient. Logic may allow us to distinguish between good and bad reasoning, but an argument can be logically consistent and have wrong conclusions if it starts from false premises. Logic doesn’t preclude ignorance.)

Now, if you want to show that logic is reliable, you can’t use logical argument to prove it — that would be using the validity of X to prove that X is valid. You would have to start from the position that logic may or not be reliable. From this position, how would we distinguish a correct argument for reliable logic from a bad one? That is, if we start by assuming that maybe we can’t distinguish good arguments from bad, any argument for anything at all will have indeterminate truth-value. Let me emphasize what I mean by indeterminate: if you can’t tell whether or not an argument is sound or invalid, then there is effectively no difference. If you can’t see, then blue and red are indistinguishable.

Now let’s recap: in order to answer the question, “Is logic reliable?”, one must begin without assuming that logic is reliable. This question proposes that perhaps there is no observable difference between good and bad arguments, and then it asks for someone to argue that this is not so. The question assumes that questions may not be answerable, thereby invalidating itself.

As for the idea that God is the guarantor of all truths, well, the best argument against that is that God doesn’t exist and hence can’t guarantee a cell-phone warranty let alone all of everything true.

Posted: August 19th 2007

See all questions answered by George Locke

John Sargeant www

Even when looking at logic theory, there have been developments, for example “Russell’s Paradox”


The idea to make something reliable is to recognise where assumptions come from, empirical observation and predictive qualities.

In this sense to invoke god in your list of assumptions is considered a cop out. This is largely because the existence or otherwise of such a being does not change what is happening in the world- “God is, as it were, the sewer into which all contradictions flow.” (Hegel)

It is true that there is more to logic theory than may at first appear apparent in common usage. I would argue that it is the method by which you can test some one’s theory or assumptions that makes logic reliable – rather than by logic can we answer the ultimate questions of life, the universe and everything. Logic is a safety check on whether something is based on rational reasoning.

Does that leave room for god justifying the suppositions we hold dear? No, it seems to be a “red card” way of ending discussion, debate and analysis.

Posted: August 18th 2007

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brian thomson www

Do people (atheists or otherwise) really assume the reliability of Logic? Your question assumes that atheists make that assumption – it’s a leading question, and it doesn’t define what you mean by Logic.

Do we even agree on what Logic is? I like the definition here:
bq. Logic, strictly speaking, is the science or study of how to evaluate arguments and reasoning.

I would expand on that by saying: like other sciences, logic is a human invention, and it needs no supernatural designer to guarantee its reliability. Also like science, it is not this “body of work” that just came in to being: it is a method, or a set of principles, developed by people to help them understand the world around them. A lot of work went into making it what it is today.

Logic is not an end in itself, it is a means to an end. We judge it by the consistent results it has delivered, over the centuries: we can say it’s reliable, in the same way that a car with 1,000,000 miles on the clock is reliable.

Beyond that, it’s not clear what is “behind” this question. Is it the suggestion of some kind of “universal logic” that can only come from an “intelligent designer”? If so, that theist will be disappointed, since the development of logic is documented in exacting detail, by uncounted writers and philosophers, all the way back to ancient India, Greece, and China.

Note the absence of Biblical references in the history of Logic: as the Old Testament describes them, the Israelites, being a theistic people, felt little need to examine the logic (or lack of) behind the orders they received from their god or their religious leaders. Those who did, such as Jonah, were reportedly punished for doing so.

That the “swallowed by a whale” story was believed is an example of just how much logic was in evidence, in that place and time. Instead, we look further west, to ancient Greece, for the formal development of modern logic, in Aristotle’s Organon, which was revived by early Islamic scholars.

Posted: August 18th 2007

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